The present invention, in some embodiments thereof, relates to a method for a receiver in a communication system to estimate phase of a carrier wave and, more particularly, but not exclusively, to estimate phase of a carrier wave in a QAM modulation receiver, and more particularly, but not exclusively, to estimate phase of a carrier wave in a PSK modulation receiver.
Estimation of carrier phase in receivers for QAM modulations has been traditionally done using a decision-directed PLL. The carrier phase recovery is based on decisions regarding the transmitted symbols. When no decision errors are made this method provides excellent performance. However, decision errors occasionally drive the PLL from its stable operating point in a process known as cycle-slip. A remedy was proposed recently by methods using pilot symbols, which are known at the receivers, to estimate carrier phase recovery. No decision errors are made at the pilot symbols.
Published US patent application 2005/0111603 of Ginesi et al proposes a process for providing a phase synchronization of a pilot aided carrier of an input digital signal z(k), the signal z(k) having signal fields of LS symbol signals, namely a block of LP pilot symbol signals ZP(k) and a data field of (LS-LP) data symbol signals Zd(k), and characterized for each signal field (l) by:
extracting the pilot symbol signals ZP(k) and
calculating an unwrapped phase estimate {circumflex over (θ)}(1LS) over the pilot block of said signal field (l) and:
interpolating said unwrapped phase estimates of successive signal fields (l, l+1 . . . ) with a Wiener interpolator having M taps to obtain interpolated phase estimates having a Minimum Mean Square Error;
providing linear interpolation between said interpolated phase estimates to obtain phase correction estimates ({circumflex over (θ)}(kS)) over the data field of said signal fields;
calculating from said phase correction estimates ({circumflex over (θ)}(kS)) a phase correction (e−j{circumflex over (θ)}(kS)) to be applied to said signal Z(k).
Additional background art includes:
David L. Donoho, “Denoising by Soft Thresholding”, IEEE Transactions on Information Theory, vol. 41, no. 3, May 1995, pp. 613-627.